How to connect one pano to multiple panos using Google street view publish API?

I'm using photo.update request for panos(360 panoramic images) connection in python. I'm able to do only connect one pano to another pano but I want to connect one pano to multiple panos. I'm not getting a successful result.

I have sent the following photoUpdate request using Python:

update_photo_url = 'https://streetviewpublish.googleapis.com/v1/photo/{}?key={}&updateMask=connections'.format("pano_1","AIzdesdfyxscvvvvvvvvvvvvvvv")

headers = {"Authorization": "Bearer {}".format("ya29.Glx6BO91jWbjzLQKYPvP16fhT-jyOEnIdnoRcZcU9uYCqzwH3Dkuf-qf_kzUc2ykYOyVTZCfaGjOEAScsJK7WgS4NE9gfS6bSobWDIMdfpfY7SPzRMmxi4kfTrmsRQ"), "Content-Length": "0", "Content-Type": "application/json"}

update_body = {
[
{
"photo": {
  "photoId": {
    "id": "pano_1"
  },
  "connections": {
    "target": {
      "id": "pano_2"
    },
    "target": {
      "id": "pano_3"
    }
  },
}
}
]
}
update_response = requests.put(update_photo_url,headers=headers,json=update_body)
update_response.text  

Error:

{
    "error": {
        "code": 400,
        "message": "Invalid JSON payload received. Unknown name \"\": Root element must be a message.",
        "status": "INVALID_ARGUMENT",
        "details": [
            {
                "@type": "type.googleapis.com/google.rpc.BadRequest",
                "fieldViolations": [
                    {
                        "description": "Invalid JSON payload received. Unknown name \"\": Root element must be a message."
                    }
                ]
            }
        ]
    }
}  

Anyone know about, How to connect multiple 360 panos from the source pano? It would be really great if someone could clarify on the possibility of it.Thanks in advance.

I've seen that your request URL is:

https://streetviewpublish.googleapis.com/v1/photo/{}?key={}&updateMask=connections'.format("pano_1","AIzdesdfyxscvvvvvvvvvvvvvvv")

In order to connect multiple photos, you need to use the batchUpdate method.

HTTP request

POST https://streetviewpublish.googleapis.com/v1/photos:batchUpdate?

Here's a sample request using curl:

curl --request POST \
    --url 'https://streetviewpublish.googleapis.com/v1/photos:batchUpdate' \
    --header 'Authorization: Bearer YOUR_ACCESS_TOKEN' \
     --header 'Content-Type: application/json' \
     --data '{
              "updatePhotoRequests": [
            {
            "updateMask": "connections",
               "photo": {
                "photoId": {
                   "id": "pano_1"
                },
                "connections": [
                   {
                       "target": {
                        "id": "pano_2"
                         }
                           },
                           {
                       "target": {
                        "id": "pano_3"
                             }
                           }
                        ]
                        }
                   }
                ]
              }'

Update: If I have four panos and I want to connect pano_1 -> pano_2, pano_3 and pano_3 -> pano_4 then what will be the json format?

You should make pano_4 as your target to be connected to pano_3.

{
  "updatePhotoRequests": [
    {
      "updateMask": "connections",
      "photo": {
        "photoId": {
          "id": "pano_3"
        },
        "connections": [
          {
            "target": {
              "id": "pano_4"
            }
          },
        ]
      }
    }
  ]
}

Just be noted that the id should be photoId of the uploaded photo.